Method of manufacturing semiconductor device

ABSTRACT

The semiconductor manufacturing method comprises the step of forming a metal alloy film of an alloy of a metal of Ni or others and a noble metal over a semiconductor substrate containing a region where silicon is partially exposed; the step of selectively reacting the silicon in the region and the metal alloy film by thermal processing to form metal silicide film containing the metal of Ni or others and the noble metal on the region; and the step of removing the metal alloy film remaining unreacted by using a solution containing hydrogen peroxide with a transition metal, which has higher ionization tendency than the metal of Ni or others, dissolved in.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2007-055494, filed on Mar. 6,2007, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a method of manufacturing asemiconductor device, more specifically, a method of manufacturing asemiconductor device which forms a metal silicide film selectively on agate electrode and source/drain regions of a MISFET.

In the recent semiconductor devices, in order to suppress the resistancerise of the electrodes to improve the drive performances, generally ametal silicide, which is low resistive, is formed on the electrodes.

Usually, the metal silicide in the electrodes are formed by selectivelysilicidizing the electrodes by the so-called salicide (self-alignedsilicide) process. salicide process is specifically a process of forminga metal film of Ni or others over a substrate surface, reacting, inregions where silicon is exposed, the metal film with the silicon bythermal processing to selectively form metal silicide film and thenremoving the metal film remaining unreacted with the silicon (refer to,e.g., Reference 1 (Japanese published unexamined patent application No.2000-091290), Reference 2 (Japanese published unexamined patentapplication No. 2004-186698) and Reference 3 (Japanese publishedunexamined patent application No. 2006-128497)).

Recently, the metal silicide is formed by using an alloy of a metal forforming the metal silicide and a noble metal added thereto. Its mostadvantageous merit is that the noble metal is suitably diffused in thegrain boundaries of the metal silicide to thereby form the metalsilicide crystal homogeneous, whereby abnormal growth of crystal grainsand phase transition can be suppressed.

However, the noble metal material is difficult to be removed with theetchants, such as sulfuric acid hydrogen peroxide mixture (SPM),hydrochloric acid hydrogen peroxide mixture and ammonia hydrogenperoxide mixture (APM), which are usually used to remove the metal filmremaining unreacted, and in the process of removing the alloy remainingunreacted, the noble metal remains as residues in the device isolationregions, etc. other than the electrodes and resultantly causesshort-circuits between the electrodes.

As a method for removing the noble metal is known to use aqua regia.However, aqua regia is seldom used in the usual semiconductormanufacturing process, and it is essential to incorporate an equipmentspecialized for the aqua regia. Unless an equipment is specialized forthe aqua regia, incidental operations, such as the addition ofspecifications of the feed and discharge of aqua regia, the tankcleaning, etc., are increased, which is a cause for operational costincrease.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided amethod of manufacturing a semiconductor device comprising: forming ametal alloy film of a metal and a noble metal over a semiconductorsubstrate having a region where silicon is partially exposed;selectively reacting by thermal processing the silicon in the regionwith the metal alloy film to form a metal silicide film containing themetal and the noble metal on the region; and removing the metal alloyfilm remaining unreacted by using a solution containing hydrogenperoxide with a transition metal, which has higher ionization tendencythan the metal, dissolved in.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C, 2A-2C and 3A-3C are sectional views showing the method ofmanufacturing the semiconductor device according to an embodiment of thepresent invention.

FIGS. 4A-4C and 5A-5C are views showing the method of removing theunreacted part of the metal alloy film in the method of manufacturingthe semiconductor device according to the embodiment of the presentinvention.

FIGS. 6A and 6B are plan views showing distributions of defects over thesilicon substrate after the unreacted part of the metal alloy film hasbeen removed.

FIG. 7 is a graph of the change of the number of defects given with thechange of the concentration of cobalt dissolved in the etching solution.

FIG. 8 is a graph of the change of the number of defects given with thechange of the concentration of titanium dissolved in the etchingsolution.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The method of manufacturing the semiconductor device according to anembodiment of the present invention will be explained with reference toFIGS. 1A-8.

FIGS. 1A-3C are sectional views showing the method of manufacturing thesemiconductor device according to the present embodiment. FIGS. 4A-5Care views showing the method of removing the unreacted part of the metalalloy film in the method of manufacturing the semiconductor deviceaccording to the present embodiment. FIGS. 6A and 6B are plan viewsshowing distributions of defects over the silicon substrate after theunreacted part of the metal alloy film has been removed. FIG. 7 is agraph of the change of the number of defects given with the change ofthe concentration of cobalt dissolved in the etching solution. FIG. 8 isa graph of the change of the number of defects given with the change ofthe concentration of titanium dissolved in the etching solution.

First, in the surface of a silicon substrate 10, a device isolation film12 for defining active regions to isolate elements from each other isformed by, e.g., STI (Shallow Trench Isolation) method.

Then, the ion implantation for the well implantation, the channel stopimplantation, the channel implantation, etc. is made to form a well 14of prescribed conductive type in the active regions of the siliconsubstrate 10 (FIG. 1A). The well 14 is, e.g., a p-well for n-channelMISFET forming region and, e.g., n-well for the p-channel MISFET formingregion.

Next, the surface of the silicon substrate 10 is thermally oxidized by,e.g., thermal oxidation method to form a gate insulating film 16 of,e.g., silicon oxide film on the active region of the silicon substrate10 defined by the device isolation film 12.

Next, over the gate insulating film 16, a polycrystalline silicon film18 is deposited by, e.g., CVD method (FIG. 1B).

Next, the polycrystalline silicon film 18 is patterned byphotolithography and dry etching to form a gate electrode 20 of thepolycrystalline silicon film 18 (FIG. 1C).

Then, ion implantation is made with the gate electrode 20 as the mask toform impurity diffused regions 22 to be extension regions or LDD regionsin the silicon substrate 10 on both sides of the gate electrode 20 (FIG.2A).

Next, silicon oxide film, for example, is deposited by, e.g., CVD methodand is etched back to form a sidewall insulating film 24 of the siliconoxide film on the side walls of the gate electrode 20 (FIG. 2B).

Next, ion implantation is made with the gate electrode 20 and thesidewall insulating film 24 as the mask to form impurity diffusedregions 26 in the silicon substrate 10 on both sides of the gateelectrode 20.

Next, rapid thermal annealing is made in, e.g., a nitrogen atmosphere toactivate the implanted impurities to form source/drain regions 28 of theimpurity diffused regions 22, 26 (FIG. 2C).

Next, over the entire surface, a metal alloy film 30 of, e.g., a 20nm-thickness of, e.g., alloy of nickel (Ni) and platinum (Pt) (NiPtalloy) is deposited by, e.g., sputtering method (FIG. 3A). NiPt alloytarget containing Pt by 5%, for example, can be used as the sputteringtarget.

Next, thermal processing is made in, e.g., a vacuum or an nitrogenatmosphere to react the metal alloy film 30 and the silicon selectivelyon the source/drain regions 28 and the gate electrode 20, where thesilicon is exposed to form metal silicide film 32 of NiPtSi on thesource/drain regions 28 and the gate electrode 20 (FIG. 3B).

Next, the metal alloy film 30 remaining unreacted with the silicon isremoved by wet etching.

Thus, by the so-called salicide process, a metal silicide film 32 ofNiPtSi is selectively formed on the gate electrode 20 and thesource/drain regions 28 of a MISFET (FIG. 3C).

In the method of manufacturing the semiconductor device described above,the step of removing the metal alloy film remaining unreacted with thesilicon by wet etching (the steps shown in FIGS. 3B and 3C) mainlycharacterizes the present invention.

The wet etching step, which is main characteristics of the presentinvention will be specifically explained with reference to FIGS. 4A to5C.

First, a chemical liquid 42 of a mixture of, e.g., sulfuric acid andhydrogen peroxide (sulfuric acid hydrogen peroxide mixture (SPM)) is fedin a chemical liquid processing bath 40 and is adjusted to a prescribedprocessing temperature, e.g., 80° C. (FIG. 4A). The SPM is a chemicalliquid generally used in the semiconductor manufacturing process.

The temperature of the chemical liquid 42 is set preferably at thetemperature usually used in the semiconductor manufacturing process,e.g., not less than 70° C. Thus, no additional manufacturing equipmentis necessary to be incorporated, and no operation cost increase iscaused.

Then, a semiconductor substrate 44 with, e.g., cobalt (Co) film 50formed on is immersed in the chemical liquid 42 in the chemical liquidprocessing bath 40 (FIG. 4B).

Thus, the cobalt formed on the semiconductor substrate 44 is dissolvedinto the chemical liquid 42. The etching solution 46 to be used inremoving the metal alloy film 30 is thus prepared (FIG. 4C).

The semiconductor substrate 44 is different from the silicon substrate10 which has been subjected to the steps of FIGS. 1A to 3B. Thesemiconductor substrate 44 can be a dummy wafer specialized indissolving cobalt into the chemical liquid 42. Otherwise, when anotherproduct using cobalt is present, and the process of manufacturing theproduct includes the step of removing the cobalt, etc. (e.g., includingthe salicide process using cobalt), the step of FIG. 4B may be made as astep of processing the product water. Otherwise, in place of immersingthe semiconductor substrate 44 with the cobalt film formed on in thechemical liquid 42, a mass of cobalt may be directly put in the chemicalliquid 42.

Next, the semiconductor substrate 44 is taken out of the chemical liquidprocessing bath 40 (FIG. 5A).

Then, the silicon substrate 10, which has been subjected to the steps upto FIG. 3B and has the metal alloy film 30 formed on is immersed in theetching solution 46 in the chemical liquid processing bath 40 (FIG. 5B).At this time, the etching solution 46 has the temperature adjusted to,e.g., 80° C., and the silicon substrate 10 is processed for, e.g., 12minutes.

Thus, the metal alloy film 30 remaining unreacted with the silicon isselectively etched by the etching solution 46, and the structure shownin FIG. 3C is formed (FIG. 5C).

Then, the silicon substrate 10 is taken out of the chemical liquidprocessing bath 40, cleaned with water and dried, is subjected to arequired manufacturing process, such as the following multilevelinterconnection process, etc., and the semiconductor device iscompleted.

FIGS. 6A and 6B are plan views of distributions of defects on thesilicon substrate after the metal alloy film has been removed. In FIG.6A, the processing chemical liquid was the etching solution of thepresent embodiment, and in FIG. 6B, the processing chemical liquid wasthe usual SPM without cobalt dissolved in. A plurality of points in thedrawings indicates the positions of the defects.

When the usual SPM was used in removing the metal alloy film 30, asshown in FIG. 6B, a number of defects are caused on the siliconsubstrate. These defects are platinum of the metal silicide film 32which has not dissolve and remained as residues in the device isolationregions, etc. In contrast to this, when the etching solution of thepresent embodiment was used, as shown in FIG. 6A, the defects on thesilicon substrate could be drastically decreased.

FIG. 7 is a graph of changes of the number of the defects with changesof the concentration of the cobalt dissolved in SPM. In the graph, thecobalt concentration is taken on the horizontal axis, and on thevertical axis, the number of the defects on the substrate surface.

As shown in FIG. 7, when the cobalt concentration in the SPM is lessthan 0.6 ppm, the effect of decreasing the defects is not sufficient. Incontrast to this, with the cobalt concentration in the SPM set at notless than 0.6 ppm, the number of the defects can be decreased by 1 placeor more.

In the above, cobalt is dissolved in the chemical liquid 42 to therebyprepare the etching solution 46, but in place of cobalt, titanium (Ti)may be used.

FIG. 8 is a graph of changes of the number of the defects with changesof the concentration of the titanium dissolved in SPM when titanium isdissolved in SPM. In the graph, the titanium concentration of theetching solution 46 is taken on the horizontal axis, and on the verticalaxis, the number of the defects on the substrate surface.

As shown in FIG. 8, when the titanium concentration in the SPM is lessthan 0.6 ppm, the effect of decreasing the defect number isinsufficient. In contrast to this, the number of the defects can bedecreased by 1 placement or more by setting the titanium concentrationat not less than 0.6 ppm.

As described above, titanium in place of cobalt is dissolved in SPM,whereby the same effect of decreasing the defects can be obtained.

Dissolving cobalt or titanium in the etching solution 46 too much willcause the risk of causing the characteristic degradation of thesemiconductor device by metal contamination, and it is preferable to setthe cobalt concentration or the titanium concentration in the etchingsolution 46 is set not more than about 10.0 ppm.

The mechanism for decreasing the residues of the platinum in removingthe metal alloy film by dissolving cobalt or titanium in SPM is notclear, but the inventor of the present invention assumes as follows.

SPM contains hydrogen peroxide (H₂O₂), and after a metal is dissolved bysulfuric acid in preparing the chemical liquid and ionized, thefollowing metal hydrate complex will be formed.

M ^(X+) +nH₂O→M(H₂O)n ^(X+1)   (1)

In forming silicide using an alloy (NiPt), in addition to a metal forforming the silicide (nickel) and a noble metal (platinum), a metalwhich has higher ionization tendency than these metals (cobalt ortitanium), have been in advance dissolved in the etching solution,whereby the metal element will form the metal hydrate complex expressedby Formula (1), and the noble metal (platinum) in the alloy will becoordinated to be thereby removed.

A metal element which has highly ionization tendency is required for thefollowing reason.

First, a metal (cobalt) which has higher ionization tendency than ametal for forming the silicide (nickel) is used, whereby the metalhydrate complex expressed by Formula (1) is formed, but the liquid has astable state (equilibrium state), which will facilitate the reaction forremoving the noble metal (platinum).

A metal (cobalt) which has higher ionization tendency than a metal forforming the silicide (nickel) is used, whereby the given metal hydratecomplex is active, and will more active on the noble metal (platinum).Inversely, when a metal element which has less ionization tendency thana metal (nickel) for forming the silicide is used, the given metalhydrate complex is less active and less reactive, and will not be ableto remove the noble metal element.

In consideration of the above-described mechanism, as the chemicalliquid for dissolve a metal element which has highly ionizationtendency, an inorganic solution containing hydrogen peroxide, e.g., amixture liquid of hydrochloric acid and hydrogen peroxide water (HPM) ora mixture liquid of ammonia and hydrogen peroxide water (APM) areexpected to produce the same effect.

It is preferable that the mixing ratio of hydrogen peroxide in theetching liquid is 10-30% for SPM and about 50% for HPM and APM. Theseranges of the mixing ratios are for setting the concentrations whichmake the activity of the respective mixture liquids highest to therebymost efficiently remove the metal for forming the silicide of the metalfilm 30 remaining unreacted with the silicon.

As described above, according to the present embodiment, in the methodof manufacturing the semiconductor device including the step of formingmetal silicide with an alloy containing a metal, such as Ni or others,and a noble metal, the alloy remaining unreacted is removed with aninorganic solution containing hydrogen peroxide and with a transitionmetal which has higher ionization tendency than the metal, whereby thealloy remaining unreacted can be removed without forming residues of thenoble metal. The solution containing hydrogen peroxide is used in theusual semiconductor manufacturing steps, and the step can be madewithout incorporation additional manufacturing equipments or withoutcausing the operation cost increase.

Modified Embodiments

The present invention is not limited to the above-described embodimentand can cover other various modifications.

For example, in the above-described embodiment, the alloy of a metal anda noble metal to be used in the salicide process is NiPt alloy. However,an alloy of the combination of another metal or another noble metal maybe used. For example, other than nickel, cobalt, titanium, zirconium(Zr), ruthenium (Ru), palladium (Pd), hafnium (Hf), tungsten (W),tantalum (Ta) or others may be used. The noble metal can be gold (Au) orothers, other than platinum.

A metal element dissolved in the etching solution can be a transitionmetal material which has higher ionization tendency than the metalforming the metal silicide. Such metal element is, e.g., scandium (Sc),vanadium (V), chrome (Cr), manganese (Mn), iron (Fe), nickel, copper(Cu), zinc (Zn), tantalum, tungsten or others.

For example, when nickel is used as the metal forming the metalsilicide, the metal element dissolved in the etching solution can be,e.g., cobalt or titanium, as described above. When cobalt is used as themetal forming the metal silicide, the metal element dissolved in theetching solution can be, e.g., titanium.

In the above-described embodiment, the etching solution is prepared bydissolving a transition metal in SPM. However, the etching solution 46may be prepared by mixing a solution with a transition metal dissolvedin sulfuric acid, and hydrogen peroxide.

In the above-described embodiment, for the batch processing, the siliconsubstrate 10 is immersed in the etching solution 46. However, thesemiconductor device manufacturing method according to the presentinvention is applicable to single wafer processing. The single waferprocessing can be made by, e.g., mixing a solution of a transition metalelement dissolved in sulfuric acid in hydrogen peroxide immediatelybefore ejected to be ejected directly to the silicon substrate with aspray or a nozzle.

In these cases as well, HPM or APM maybe used.

In the above-described embodiment, the present invention is applied tothe typical MISFET. However, the structure of the MISFET the presentinvention is applicable to is not limited to the above-describedembodiment.

For example, in the present embodiment, the metal silicide film 32 isformed on the gate electrode 20 and the source/drain regions 28.However, the silicide film 32 may be formed on either of the gateelectrode 20 and the source/drain regions 28. In this case, before thesalicide process, an insulating film (e.g., silicon oxide film orsilicon nitride film) for preventing the silicidation reaction may beformed on the source/drain regions 28 or on the gate electrode 20.

1. A method of manufacturing a semiconductor device comprising: forminga metal alloy film of a metal and a noble metal over a semiconductorsubstrate having a region where silicon is partially exposed;selectively reacting by thermal processing the silicon in the regionwith the metal alloy film to form a metal silicide film containing themetal and the noble metal on the region; and removing the metal alloyfilm remaining unreacted by using a solution containing hydrogenperoxide with a transition metal, which has higher ionization tendencythan the metal, dissolved in.
 2. The method of manufacturing asemiconductor device according to claim 1, wherein the solution is amixture liquid of sulfuric acid and hydrogen peroxide, a mixture liquidof hydrochloric acid and hydrogen peroxide, or a mixture liquid ofammonia and hydrogen peroxide.
 3. The method of manufacturing asemiconductor device according to claim 1, wherein a mixing ratio of thehydrogen peroxide is 10-30%.
 4. The method of manufacturing asemiconductor device according to claim 1, wherein a concentration ofthe transition metal in the solution is 0.6-10.0 ppm.
 5. The method ofmanufacturing a semiconductor device according to claim 1, wherein atemperature of the solution is not less than 70° C.
 6. The method ofmanufacturing a semiconductor device according to claim 1, furthercomprising the step of: immersing the solution another semiconductorsubstrate with the transition metal formed on to thereby dissolve thetransition metal into the solution.
 7. The method of manufacturing asemiconductor device according to claim 1, wherein the metal is nickel,and the transition metal is cobalt or titanium
 8. The method ofmanufacturing a semiconductor device according to claim 1, wherein themetal is cobalt, and the transition metal is titanium.
 9. The method ofmanufacturing a semiconductor device according to claim 1, wherein thenoble metal is platinum or gold.
 10. The method of manufacturing asemiconductor device according to claim 1, wherein the region is a gateelectrode or the source/drain regions of a MISFET.